Common Protein In Human Semen Increases Infectious Potential Of HIV

A common protein in humansemen increases the infectious potential of HIV 100,000-fold, according to astudy published Friday in the journal Cell, the San Francisco Chronicle reports (Russell, SanFrancisco Chronicle, 12/14).

Researchers at the University of Ulm in Germany began looking foringredients in human semen that could block infection with HIV-1, the mostcommon strain of the virus. The researchers instead found that the proteinprostatic acidic phosphatase, which is produced in the prostate and forms tinyfibers called amyloid fibrils, enhanced HIV transmission (Steenhuysen, Reuters, 12/13).

According to the Chronicle, the discovery could help explain whyHIV "appears weakly infectious in laboratory dishes" but "canspread explosively through sexual contact." It takes between 1,000 and100,000 HIV particles to successfully infect human cells in most labexperiments. However, when PAP was added, as few as three HIV particles caninfect human cells, the study found. Although it is unclear why the proteinincreases HIV transmission, it is possible that the amyloid fibrils attach tocell surfaces, making it easier for HIV to enter cells.

According to the Chronicle, little research has been conducted todetermine what role semen plays in the transmission of HIV. Finding a way toeliminate the protein could make HIV transmission more difficult, according tothe Chronicle. Warner Greene, director of the Gladstone Institute of Virology and Immunology, has begun a project to determinehow to block PAP, but he said that the project will not be easy. In addition, aGerman pharmaceutical company has begun early studies to determine whether aversion of PAP could be tested as a potential HIV drug (San FranciscoChronicle, 12/14). The researchers said that additional studies areneeded on the "role of amyloids in the transmission and pathogenesis ofenveloped viruses" (Reuters, 12/13).

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Frank Kirchhoff, who ledthe study, said he was "so surprised" by the finding that at first he"did not believe the numbers." He added that the researchers"did the experiment multiple times, and the results were always thesame." Greene called the finding "one of the most interesting newperspectives on HIV transmission to emerge in years."

Anthony Fauci, director of NIH's NationalInstitute for Allergy and Infectious Diseases, said that the study is impressive but thatthe findings are a long way from producing a practical solution to reduce therisk of HIV transmission. "It is a surprising finding, but I would becautious about how important this is going to be," he said. Fauci addedthat sexual contact is only one mode of HIV transmission and that it isunlikely similar proteins exist in breastmilk, which is a source ofmother-to-child HIV transmission.

Ian McGowan, a researcher at the University ofPittsburgh andprincipal investigator with the MicrobicideTrials Network,said he is skeptical that the findings would lead to advances in HIV prevention. He added that a new generationof microbicides -- which is made from antiretroviral drugs and has successfullyblocked the virus in test tube studies -- soon will enter clinical trials andcould be successful in blocking PAP and similar proteins. Jay Levy, avirologist of the University of California-SanFrancisco, said thefinding likely will to lead to further research about the role PAP plays in HIVtransmission, adding that studies could be conducted to determine PAPprevalence among populations at high risk of HIV (San Francisco Chronicle,12/14).

Reprintedwith permission from kaisernetwork.org. You can view the entire Kaiser Daily HIV/AIDS Report, search the archives, and sign upfor email delivery at kaisernetwork.org/email . The Kaiser Daily HIV/AIDS Reportis published for kaisernetwork.org, a free service of The Henry J. KaiserFamily Foundation.